The flu is a contagious respiratory illness caused by influenza viruses. It causes mild to severe illness, and at times can lead to death. Annually, in the United States, influenza is contracted by 5-20% of the population, hospitalizing about 200,000, and causing the deaths of about 36,000.
Influenza viruses spread in respiratory droplets caused by coughing and sneezing, which are usually transmitted from person to person. Immunity to influenza surface antigens, particularly hemagglutinin, reduces the likelihood of infection and severity of disease if infection occurs. Although influenza vaccines are available, because a vaccine against one influenza virus type or subtype confers limited or no protection against another type or subtype of influenza, it is necessary to incorporate one or more new strains in each year's influenza vaccine.
Influenza viruses are segmented negative-strand RNA viruses and belong to the Orthomyxoviridae family. Influenza A virus consists of 9 structural proteins and codes additionally for one nonstructural NS1 protein with regulatory functions. The non-structural NS1 protein is synthesized in large quantities during the reproduction cycle and is localized in the cytosol and nucleus of the infected cells. The segmented nature of the viral genome allows the mechanism of genetic reassortment (exchange of genome segments) to take place during mixed infection of a cell with different viral strains. The influenza A virus may be further classified into various subtypes depending on the different hemagglutinin (HA) and neuraminidase (NA) viral proteins displayed on their surface. Influenza A virus subtypes are identified by two viral surface glycoproteins, hemagglutinin (HA or H) and neuraminidase (NA or N). Each influenza virus subtype is identified by its combination of H and N proteins. There are 16 known HA subtypes and 9 known NA subtypes. Influenza type A viruses can infect people, birds, pigs, horses, and other animals, but wild birds are the natural hosts for these viruses. Only some influenza A subtypes (i.e., H1N1 H1N2, and H3N2) are currently in circulation among people, but all combinations of the 16 H and 9 NA subtypes have been identified in avian species, especially in wild waterfowl and shorebirds. In addition, there is increasing evidence that H5 and H7 influenza viruses can also cause human illness.
The HA of influenza A virus comprises two structurally distinct regions, namely, a globular head region and a stem region. The globular head region contains a receptor binding site which is responsible for virus attachment to a target cell and participates in the hemagglutination activity of HA. The stem region contains a fusion peptide which is necessary for membrane fusion between the viral envelope and an endosomal membrane of the cell and thus relates to fusion activity (Wiley et al., Ann. Rev. Biochem., 56:365-394 (1987)).
A pandemic is a global disease outbreak. An influenza pandemic occurs when a new influenza A virus: (1) emerges for which there is little or no immunity in the human population, (2) begins to cause serious illness, and then (3) spreads easily person-to-person worldwide. During the 20th century there have been three such influenza pandemics. First, in 1918, the “Spanish Flu” influenza pandemic caused at least 500,000 deaths in the United States and up to 40 million deaths worldwide. This pandemic was caused by influenza A H1N1 subtype. Second, in 1957, the “Asian Flu” influenza pandemic, caused by the influenza A H2N2 subtype, resulted in at least 70,000 deaths in the United States and 1-2 million deaths worldwide. Most recently in 1968 the “Hong Kong Flu” influenza pandemic, caused by the influenza A H3N2 subtype, resulted in about 34,000 U.S. deaths and 700,000 deaths worldwide.
In 1997, the first influenza A H5N1 cases were reported in Hong Kong. This was the first time that this type of avian virus directly infected humans, but a pandemic did not result because human to human transmission was not observed.
Lu et al., Resp. Res. 7:43 (2006) (doi: 10.1186/1465-992-7-43) report the preparation of anti-H5N1 IgGs from horses vaccinated with inactivated H5N1 virus, and of H5N1-specifc F(ab′)2 fragments, which were described to protect BALB/c mice infected with H5N1 virus.
Hanson et al., Resp. Res. 7:126 (doi: 10.1186/1465-9921-7-126) describe the use of a chimeric monoclonal antibody specific for influenza A H5 virus hemagglutinin for passive immunization of mice.
Neutralizing antibodies to influenza viruses are disclosed in U.S. Application Publication No. 20080014205, published on Jan. 17, 2008.
In view of the severity of the respiratory illness caused by certain influenza A viruses, and the threat of a potential pandemic, there is a great need for effective preventative and treatment methods. The present invention addresses this need by providing influenza A neutralizing molecules against various H subtypes of the virus, including, without limitation, the H1, and H3 subtypes, and the H5 subtype of the influenza A virus. The invention further provides molecules capable of neutralizing more than one, and preferably all, isolates (strains) of a given subtype of the influenza A virus, including, without limitation, isolates obtained from various human and non-human species and isolates from victims and/or survivors of various influenza epidemics and/or pandemics.
Such crossreactive neutralizing molecules can be used for the prevention and/or treatment influenza virus infection, including passive immunization of infected or at risk populations in cases of epidemics or pandemics. Additionally, crossreactive antibodies can be used as a design guide for future vaccine discovery and an assessment tool for current vaccine clinical development.